pub const CityHash32 = structfn fmix(h: u32) u32A 32-bit to 32-bit integer hash copied from Murmur3.
fn rotr32(x: u32, comptime r: u32) u32Rotate right helper
fn mur(a: u32, h: u32) u32Helper from Murmur3 for combining two 32-bit values.
fn hash32Len0To4(str: []const u8) u32fn hash32Len5To12(str: []const u8) u32fn hash32Len13To24(str: []const u8) u32pub fn hash(str: []const u8) u3216
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168pub const CityHash32 = struct {
const Self = @This();
// Magic numbers for 32-bit hashing. Copied from Murmur3.
const c1: u32 = 0xcc9e2d51;
const c2: u32 = 0x1b873593;
// A 32-bit to 32-bit integer hash copied from Murmur3.
fn fmix(h: u32) u32 {
var h1: u32 = h;
h1 ^= h1 >> 16;
h1 *%= 0x85ebca6b;
h1 ^= h1 >> 13;
h1 *%= 0xc2b2ae35;
h1 ^= h1 >> 16;
return h1;
}
// Rotate right helper
fn rotr32(x: u32, comptime r: u32) u32 {
return (x >> r) | (x << (32 - r));
}
// Helper from Murmur3 for combining two 32-bit values.
fn mur(a: u32, h: u32) u32 {
var a1: u32 = a;
var h1: u32 = h;
a1 *%= c1;
a1 = rotr32(a1, 17);
a1 *%= c2;
h1 ^= a1;
h1 = rotr32(h1, 19);
return h1 *% 5 +% 0xe6546b64;
}
fn hash32Len0To4(str: []const u8) u32 {
const len: u32 = @as(u32, @truncate(str.len));
var b: u32 = 0;
var c: u32 = 9;
for (str) |v| {
b = b *% c1 +% @as(u32, @bitCast(@as(i32, @intCast(@as(i8, @bitCast(v))))));
c ^= b;
}
return fmix(mur(b, mur(len, c)));
}
fn hash32Len5To12(str: []const u8) u32 {
var a: u32 = @as(u32, @truncate(str.len));
var b: u32 = a *% 5;
var c: u32 = 9;
const d: u32 = b;
a +%= fetch32(str.ptr, 0);
b +%= fetch32(str.ptr, str.len - 4);
c +%= fetch32(str.ptr, (str.len >> 1) & 4);
return fmix(mur(c, mur(b, mur(a, d))));
}
fn hash32Len13To24(str: []const u8) u32 {
const len: u32 = @as(u32, @truncate(str.len));
const a: u32 = fetch32(str.ptr, (str.len >> 1) - 4);
const b: u32 = fetch32(str.ptr, 4);
const c: u32 = fetch32(str.ptr, str.len - 8);
const d: u32 = fetch32(str.ptr, str.len >> 1);
const e: u32 = fetch32(str.ptr, 0);
const f: u32 = fetch32(str.ptr, str.len - 4);
return fmix(mur(f, mur(e, mur(d, mur(c, mur(b, mur(a, len)))))));
}
pub fn hash(str: []const u8) u32 {
if (str.len <= 24) {
if (str.len <= 4) {
return hash32Len0To4(str);
} else {
if (str.len <= 12)
return hash32Len5To12(str);
return hash32Len13To24(str);
}
}
const len: u32 = @as(u32, @truncate(str.len));
var h: u32 = len;
var g: u32 = c1 *% len;
var f: u32 = g;
const a0: u32 = rotr32(fetch32(str.ptr, str.len - 4) *% c1, 17) *% c2;
const a1: u32 = rotr32(fetch32(str.ptr, str.len - 8) *% c1, 17) *% c2;
const a2: u32 = rotr32(fetch32(str.ptr, str.len - 16) *% c1, 17) *% c2;
const a3: u32 = rotr32(fetch32(str.ptr, str.len - 12) *% c1, 17) *% c2;
const a4: u32 = rotr32(fetch32(str.ptr, str.len - 20) *% c1, 17) *% c2;
h ^= a0;
h = rotr32(h, 19);
h = h *% 5 +% 0xe6546b64;
h ^= a2;
h = rotr32(h, 19);
h = h *% 5 +% 0xe6546b64;
g ^= a1;
g = rotr32(g, 19);
g = g *% 5 +% 0xe6546b64;
g ^= a3;
g = rotr32(g, 19);
g = g *% 5 +% 0xe6546b64;
f +%= a4;
f = rotr32(f, 19);
f = f *% 5 +% 0xe6546b64;
var iters = (str.len - 1) / 20;
var ptr = str.ptr;
while (iters != 0) : (iters -= 1) {
const b0: u32 = rotr32(fetch32(ptr, 0) *% c1, 17) *% c2;
const b1: u32 = fetch32(ptr, 4);
const b2: u32 = rotr32(fetch32(ptr, 8) *% c1, 17) *% c2;
const b3: u32 = rotr32(fetch32(ptr, 12) *% c1, 17) *% c2;
const b4: u32 = fetch32(ptr, 16);
h ^= b0;
h = rotr32(h, 18);
h = h *% 5 +% 0xe6546b64;
f +%= b1;
f = rotr32(f, 19);
f = f *% c1;
g +%= b2;
g = rotr32(g, 18);
g = g *% 5 +% 0xe6546b64;
h ^= b3 +% b1;
h = rotr32(h, 19);
h = h *% 5 +% 0xe6546b64;
g ^= b4;
g = @byteSwap(g) *% 5;
h +%= b4 *% 5;
h = @byteSwap(h);
f +%= b0;
const t: u32 = h;
h = f;
f = g;
g = t;
ptr = offsetPtr(ptr, 20);
}
g = rotr32(g, 11) *% c1;
g = rotr32(g, 17) *% c1;
f = rotr32(f, 11) *% c1;
f = rotr32(f, 17) *% c1;
h = rotr32(h +% g, 19);
h = h *% 5 +% 0xe6546b64;
h = rotr32(h, 17) *% c1;
h = rotr32(h +% f, 19);
h = h *% 5 +% 0xe6546b64;
h = rotr32(h, 17) *% c1;
return h;
}
}